Molding is a process by virtue of which a molded article can be formed from molding material by using a molding system. Various molded articles can be formed by using the molding process, such as an injection molding process. One example of a molded article that can be formed, for example, from polyethylene terephthalate (PET) material is a preform that is capable of being subsequently blown into a beverage container, such as, a bottle and the like.
As an illustration, injection molding of PET material involves heating the PET material (or other suitable molding material for that matter) to a homogeneous molten state and injecting, under pressure, the so-melted PET material into a molding cavity defined, at least in part, by a female cavity piece and a male core piece mounted respectively on a cavity plate and a core plate of a mold. The cavity plate and the core plate are urged together and are held together by clamp force, the clamp force being sufficient to keep the cavity and the core pieces together against the pressure of the injected PET material. The molding cavity has a shape that substantially corresponds to a final cold-state shape of the molded article to be molded. The so-injected PET material is then cooled to a temperature sufficient to enable ejection of the so-formed molded article from the molding cavity. When cooled, the molded article shrinks inside of the molding cavity and, as such, when the cavity and core plates are urged apart, the molded article tends to remain associated with the core piece. Accordingly, by urging the core plate away from the cavity plate, the molded article can be subsequently demolded by ejecting it off the core piece. Ejection structures are known to assist in removing the molded articles from the core halves. Examples of the ejection structures include stripper plates, stripper rings and neck ring, ejector pins, etc.
When dealing with molding a preform that is capable of being subsequently blown into a beverage container, one consideration that needs to be addressed is forming a so-called “neck region”. Typically and as an example, the neck region includes (i) threads (or other suitable structure) for accepting and retaining a closure assembly (ex. a bottle cap), and (ii) an anti-pilferage assembly to cooperate, for example, with the closure assembly to indicate whether the end product (i.e. the beverage container that has been filled with a beverage and shipped to a store) has been tampered with in any way. The neck region may comprise other additional elements used for various purposes, for example, to cooperate with parts of the molding system (ex. a support ledge, etc.). As is appreciated in the art, the neck region can not be easily formed by using the cavity and core halves. Traditionally, split mold inserts (sometimes referred to by those skilled in the art as “neck ring”) have been used to form the neck region.
With reference to FIG. 1, a section along a portion of an injection mold 50 illustrates a typical molding insert stack assembly 52 that can be arranged (in use) within a molding machine (not depicted). The description of FIG. 1 that will be presented herein below will be greatly simplified, as it is expected that one skilled in the art will appreciate configuration of other components of the injection mold 50 that will not be discussed in the following description.
The molding insert stack assembly 52 includes a split mold insert pair 54 that together with a mold cavity insert 56, a gate insert 58 and a core insert 60 defines a molding cavity 62. Molding material can be injected into the molding cavity 62 from a source of molding material (not depicted) via a receptacle (not separately numbered) in the gate insert 58 to form a molded article. In order to facilitate forming of the neck region of the molded article and subsequent removal of the molded article therefrom, the split mold insert pair 54 comprises a pair of complementary split mold inserts (not separately numbered) that are mounted on adjacent slides of a slide pair (not depicted). The slide pair is slidably mounted on a top surface of a stripper plate (not depicted). As commonly known, and as, for example, generally described in U.S. Pat. No. 6,799,962 to Mai et al (granted on Oct. 5, 2004), the stripper plate (not depicted) is configured to be movable relative to the cavity insert 56 and the core insert 60, when the mold is arranged in an open configuration, whereby the slide pair, and the complementary split mold inserts mounted thereon, can be laterally driven, via a cam arrangement (not shown) or any other suitable known means, for the release of the molded article from the molding cavity 62.
Several types of the split mold insert pair 54 are known in the art. For example, the split mold insert pair 54 can be of a cavity-lock type or a core-lock type (depicted in FIG. 1), depending on an arrangement that is used for locking the split mold insert pair 54, in use, relative to the mold cavity insert 56 and the core insert 60. The split mold insert pair 54 can also define a portion of the neck region (as is the case in FIG. 1) or the whole of the neck region or, put another way, “encapsulate” the neck region. One of the functions performed by the split mold insert pair 54 is to assist in ejecting the molded article off the core insert 60 by “sliding” the molded article off the core insert 60.
An example of the latter is disclosed in a co-owned U.S. Pat. No. 6,989,124 issued on Jan. 24, 2006 to Miller et al., which teaches an injection molding method and apparatus for ejecting a molded plastic article from a mold. A lifting structure and/or step is provided with a lifting portion which is configured to contact substantially one half of an end of the molded plastic article along a line substantially perpendicular to the lifting direction. Since the molded plastic article is lifted by its end, the article does not have to be solidified at its interior, thus allowing earlier removal of the article from the mold, reducing cycle time. A tapered surface forms an acute angle with respect to the lifting portion to form a tight seal with the mold, preventing leakage. Preferably, the neck ring engages only an outer circumferential portion of the molded plastic article during a majority of a mold opening stroke.
Co-owned U.S. Pat. No. 7,128,865 issued to Martin on Oct. 31, 2006 discloses an injection molding method and apparatus for ejecting a molded plastic preform from a mold. A first lifting structure and/or step is configured to have an inner surface with an area for sealing and aligning with a complementary surface on a core, and to have an upper surface with an area for sealing and aligning with a complementary surface on a second lifting structure, said upper surface of said first lifting structure being configured to lift a molded plastic preform from the injection mold in a lifting direction for a first period of time, the lower portion of the molded plastic preform lying in a plane substantially perpendicular to the lifting direction. A second lifting structure and/or step is configured to have an inner surface configured to lift an outer surface of the molded plastic preform from the injection mold in the lifting direction for a second period of time, the outer surface of the molded plastic preform including structure lying in a plane substantially parallel with the lifting direction. Since the molded plastic preform is lifted by its end, the preform does not have to be solidified at its interior, thus allowing earlier removal of the preform from the mold, reducing cycle time.